1. Field of the Invention
The present invention relates to an auto-tensioner, and in particular to an auto-tensioner used to apply proper tension to an engine timing belt for an automobile or a belt for driving an auxiliary machinery such as an alternator or a compressor (hereinafter referred to as simply "belt" in both cases).
2. Description of the Prior Art
Conventionally, an auto-tensioner of the type illustrated in FIG. 3 and FIG. 4, for example, is used to apply proper tension to a belt. A tubular fixed shaft 1 is secured e.g. to the front surface of an engine cylinder block by a bolt (omitted from the drawings). A half-casing 2 is secured on the base end section (left end in FIG. 3) of the fixed shaft 1 concentric to the fixed shaft 1, and an engaging projection 3 is secured to the axially outer end surface of the half-casing 2. The engaging projection 3 is to be engaged with an engaging indentation (not shown) formed on the front surface of the cylinder block to prevent the rotation of the fixed shaft 1.
A cylindrical section 5 provided on a rocker member 4 is externally fitted on this fixed shaft 1 through a sliding bearing 6 therebetween. A rocker arm 7 extends radially outward from the cylindrical section 5, and a pivot shaft 8 is provided on the tip of the rocker arm 7, parallel to the fixed shaft 1. A tension pulley 9 is pivotally supported on the pivot shaft 8 by means of a rolling bearing 10.
A half-casing 11 is provided on one part of the rocker member 4, concentric with the cylindrical section 5. A case 14 for enclosing a torsion coil spring 13 is formed by combining the half-casing 11 and the half-casing 2 in a nested shape.
One end of the torsion coil spring 13 is engaged with the half-casing 2 on the side of the fixed shaft 1 with the other end engaged with the half-casing 11 on the side of the rocker member 4 to impart an elastic force on the rocker member 4 in a direction to force the tension pulley 9 elastically toward a belt. Accordingly, the tension on the belt is normally maintained at a uniform level with the tension pulley 9 being pressed against the belt, regardless of any changes in the dimensions of the belt from a temperature change or the like, or vibration or the like from the operation of the engine.
Further, the inner peripheral edge section of a damper plate 15 is secured to the outer periphery of the axial tip portion (the right end in FIG. 3) of the fixed shaft 1, so that the outer peripheral edge section of the damper plate 15 slides on one part of the inner peripheral surface of the rocker member 4. Specifically, the damper plate 15 is fabricated together with the fixed shaft 1 and the half-casing 2 e.g. by die-cast forming from aluminum. A rectangular tubular section 16 is formed on the outer peripheral surface of the axial tip of the fixed shaft 1, and a rectangular hole 17 is formed at the center of the damper plate 15 to receive the rectangular tubular section 16 inserted thereinto. The axial tip of the rectangular tubular section 16 is then deformed by caulking or crimping against the peripheral edge section of the rectangular hole 17 to form caulked or crimped sections 18 so that the damper plate 15 is non-rotatably secured to the axial tip of the fixed shaft 1 from the effect of the caulked or crimped sections 18.
In this manner, an annular clearance space 19 is provided axially between the damper plate 15 and the rocker member 4 with the damper plate 15 secured to the axial tip portion of the fixed shaft 1. An 0-ring 21 is fitted into an indented annular groove 20 formed over the entire periphery on the outer peripheral surface of the damper plate 15 in either axial end section thereof. The outer peripheral edges of the 0-rings 21 is adapted to slide on the inner peripheral surface of the rocker member 4 to liquid-tightly close off the two end sections of the clearance space 19.
A viscous fluid 22 such as silicone oil or the like is filled into this clearance space 19 through a filling hole 23. The filling hole 23 is closed off by the insertion of a steel ball 24, after the filling operation.
In this manner, the viscous fluid 22 is sealingly enclosed in the clearance space 19 which is present between the fixed shaft 1, specifically the damper plate 15 and the rocker member 4 which are relatively displaced in the direction of rotation. Accordingly, when the belt vibrates with a small amplitude during the operation of the engine, this vibration, transmitted to both the tension pulley 9 and the rocker member 4, is damped by the viscous fluid 22 in the clearance space 19, so that the vibration of the tension pulley 9 and the rocker member 4 does not grow.
The present invention is designed to eliminate any backlash in the engaged section of the damper plate 15 with respect to the fixed shaft 1 without increasing the fabrication costs of the auto-tensinor with the structure and operation described above.
Conventionally, in order that the damper plate 15 is secured to the fixed shaft 1 so as not to rotate, the rectangular tubular section 16 on the axial tip portion of the fixed shaft 1 is formed simultaneously with the fabrication by die-casting of the fixed shaft 1, while the rectangular hole 17 in the center section of the damper plate 15 is formed simultaneously with the fabrication by die-casting of damper plate 15. Accordingly, because of unavoidable fabrication errors, backlashes are produced unavoidably in the engaged section when the rectangular tubular section 16 and the rectangular hole 17 are fitted together. Therefore, there are occasions where these backlashes cannot be eliminated, even when the caulked or crimped sections 18 are formed on the axial tip portion of the rectangular tubular section 16.
If the dimensional precision of the rectangular tubular section 16 and the rectangular hole 17 is improved by not using die-casting as the fabrication method, but rather forming by a machining process such as a shaper process or the like, the degree of backlash production in the above-mentioned engaged section would be reduced, so that it is possible to completely eliminate the backlashes in the engaged section by providing the caulked sections 18. But this is not desirable because the cost of fabrication is increased.